This is elisp, produced by makeinfo version 4.0f from ./elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This Info file contains edition 2.8 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 21.2. Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Copying", with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."  File: elisp, Node: Buffers and Windows, Next: Displaying Buffers, Prev: Cyclic Window Ordering, Up: Windows Buffers and Windows =================== This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. *Note Displaying Buffers::, for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control. - Function: set-window-buffer window buffer-or-name This function makes WINDOW display BUFFER-OR-NAME as its contents. It returns `nil'. This is the fundamental primitive for changing which buffer is displayed in a window, and all ways of doing that call this function. (set-window-buffer (selected-window) "foo") => nil - Function: window-buffer &optional window This function returns the buffer that WINDOW is displaying. If WINDOW is omitted, this function returns the buffer for the selected window. (window-buffer) => # - Function: get-buffer-window buffer-or-name &optional all-frames This function returns a window currently displaying BUFFER-OR-NAME, or `nil' if there is none. If there are several such windows, then the function returns the first one in the cyclic ordering of windows, starting from the selected window. *Note Cyclic Window Ordering::. The argument ALL-FRAMES controls which windows to consider. * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is 0, consider windows on all visible or iconified frames. * If it is a frame, consider windows on that frame. - Function: get-buffer-window-list buffer-or-name &optional minibuf all-frames This function returns a list of all the windows currently displaying BUFFER-OR-NAME. The two optional arguments work like the optional arguments of `next-window' (*note Cyclic Window Ordering::); they are _not_ like the single optional argument of `get-buffer-window'. Perhaps we should change `get-buffer-window' in the future to make it compatible with the other functions. The argument ALL-FRAMES controls which windows to consider. * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is 0, consider windows on all visible or iconified frames. * If it is a frame, consider windows on that frame. - Variable: buffer-display-time This variable records the time at which a buffer was last made visible in a window. It is always local in each buffer; each time `set-window-buffer' is called, it sets this variable to `(current-time)' in the specified buffer (*note Time of Day::). When a buffer is first created, `buffer-display-time' starts out with the value `nil'.  File: elisp, Node: Displaying Buffers, Next: Choosing Window, Prev: Buffers and Windows, Up: Windows Displaying Buffers in Windows ============================= In this section we describe convenient functions that choose a window automatically and use it to display a specified buffer. These functions can also split an existing window in certain circumstances. We also describe variables that parameterize the heuristics used for choosing a window. *Note Buffers and Windows::, for low-level functions that give you more precise control. All of these functions work by calling `set-window-buffer'. Do not use the functions in this section in order to make a buffer current so that a Lisp program can access or modify it; they are too drastic for that purpose, since they change the display of buffers in windows, which would be gratuitous and surprise the user. Instead, use `set-buffer' and `save-current-buffer' (*note Current Buffer::), which designate buffers as current for programmed access without affecting the display of buffers in windows. - Command: switch-to-buffer buffer-or-name &optional norecord This function makes BUFFER-OR-NAME the current buffer, and also displays the buffer in the selected window. This means that a human can see the buffer and subsequent keyboard commands will apply to it. Contrast this with `set-buffer', which makes BUFFER-OR-NAME the current buffer but does not display it in the selected window. *Note Current Buffer::. If BUFFER-OR-NAME does not identify an existing buffer, then a new buffer by that name is created. The major mode for the new buffer is set according to the variable `default-major-mode'. *Note Auto Major Mode::. Normally the specified buffer is put at the front of the buffer list (both the selected frame's buffer list and the frame-independent buffer list). This affects the operation of `other-buffer'. However, if NORECORD is non-`nil', this is not done. *Note The Buffer List::. The `switch-to-buffer' function is often used interactively, as the binding of `C-x b'. It is also used frequently in programs. It always returns `nil'. - Command: switch-to-buffer-other-window buffer-or-name &optional norecord This function makes BUFFER-OR-NAME the current buffer and displays it in a window not currently selected. It then selects that window. The handling of the buffer is the same as in `switch-to-buffer'. The currently selected window is absolutely never used to do the job. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well. This function updates the buffer list just like `switch-to-buffer' unless NORECORD is non-`nil'. - Function: pop-to-buffer buffer-or-name &optional other-window norecord This function makes BUFFER-OR-NAME the current buffer and switches to it in some window, preferably not the window previously selected. The "popped-to" window becomes the selected window within its frame. If the variable `pop-up-frames' is non-`nil', `pop-to-buffer' looks for a window in any visible frame already displaying the buffer; if there is one, it returns that window and makes it be selected within its frame. If there is none, it creates a new frame and displays the buffer in it. If `pop-up-frames' is `nil', then `pop-to-buffer' operates entirely within the selected frame. (If the selected frame has just a minibuffer, `pop-to-buffer' operates within the most recently selected frame that was not just a minibuffer.) If the variable `pop-up-windows' is non-`nil', windows may be split to create a new window that is different from the original window. For details, see *Note Choosing Window::. If OTHER-WINDOW is non-`nil', `pop-to-buffer' finds or creates another window even if BUFFER-OR-NAME is already visible in the selected window. Thus BUFFER-OR-NAME could end up displayed in two windows. On the other hand, if BUFFER-OR-NAME is already displayed in the selected window and OTHER-WINDOW is `nil', then the selected window is considered sufficient display for BUFFER-OR-NAME, so that nothing needs to be done. All the variables that affect `display-buffer' affect `pop-to-buffer' as well. *Note Choosing Window::. If BUFFER-OR-NAME is a string that does not name an existing buffer, a buffer by that name is created. The major mode for the new buffer is set according to the variable `default-major-mode'. *Note Auto Major Mode::. This function updates the buffer list just like `switch-to-buffer' unless NORECORD is non-`nil'. - Command: replace-buffer-in-windows buffer This function replaces BUFFER with some other buffer in all windows displaying it. The other buffer used is chosen with `other-buffer'. In the usual applications of this function, you don't care which other buffer is used; you just want to make sure that BUFFER is no longer displayed. This function returns `nil'.  File: elisp, Node: Choosing Window, Next: Window Point, Prev: Displaying Buffers, Up: Windows Choosing a Window for Display ============================= This section describes the basic facility that chooses a window to display a buffer in--`display-buffer'. All the higher-level functions and commands use this subroutine. Here we describe how to use `display-buffer' and how to customize it. - Command: display-buffer buffer-or-name &optional not-this-window frame This command makes BUFFER-OR-NAME appear in some window, like `pop-to-buffer', but it does not select that window and does not make the buffer current. The identity of the selected window is unaltered by this function. If NOT-THIS-WINDOW is non-`nil', it means to display the specified buffer in a window other than the selected one, even if it is already on display in the selected window. This can cause the buffer to appear in two windows at once. Otherwise, if BUFFER-OR-NAME is already being displayed in any window, that is good enough, so this function does nothing. `display-buffer' returns the window chosen to display BUFFER-OR-NAME. If the argument FRAME is non-`nil', it specifies which frames to check when deciding whether the buffer is already displayed. If the buffer is already displayed in some window on one of these frames, `display-buffer' simply returns that window. Here are the possible values of FRAME: * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is 0, consider windows on all visible or iconified frames. * If it is a frame, consider windows on that frame. Precisely how `display-buffer' finds or creates a window depends on the variables described below. - User Option: display-buffer-reuse-frames If this variable is non-`nil', `display-buffer' searches existing frames for a window displaying the buffer. If the buffer is already displayed in a window in some frame, `display-buffer' makes the frame visible and raises it, to use that window. If the buffer is not already displayed, or if `display-buffer-reuse-frames' is `nil', `display-buffer''s behavior is determined by other variables, described below. - User Option: pop-up-windows This variable controls whether `display-buffer' makes new windows. If it is non-`nil' and there is only one window, then that window is split. If it is `nil', then `display-buffer' does not split the single window, but uses it whole. - User Option: split-height-threshold This variable determines when `display-buffer' may split a window, if there are multiple windows. `display-buffer' always splits the largest window if it has at least this many lines. If the largest window is not this tall, it is split only if it is the sole window and `pop-up-windows' is non-`nil'. - User Option: even-window-heights This variable determines if `display-buffer' should even out window heights if the buffer gets displayed in an existing window, above or beneath another existing window. If `even-window-heights' is `t', the default, window heights will be evened out. If `even-window-heights' is `nil', the orginal window heights will be left alone. - User Option: pop-up-frames This variable controls whether `display-buffer' makes new frames. If it is non-`nil', `display-buffer' looks for an existing window already displaying the desired buffer, on any visible frame. If it finds one, it returns that window. Otherwise it makes a new frame. The variables `pop-up-windows' and `split-height-threshold' do not matter if `pop-up-frames' is non-`nil'. If `pop-up-frames' is `nil', then `display-buffer' either splits a window or reuses one. *Note Frames::, for more information. - Variable: pop-up-frame-function This variable specifies how to make a new frame if `pop-up-frames' is non-`nil'. Its value should be a function of no arguments. When `display-buffer' makes a new frame, it does so by calling that function, which should return a frame. The default value of the variable is a function that creates a frame using parameters from `pop-up-frame-alist'. - User Option: pop-up-frame-alist This variable holds an alist specifying frame parameters used when `display-buffer' makes a new frame. *Note Frame Parameters::, for more information about frame parameters. - User Option: special-display-buffer-names A list of buffer names for buffers that should be displayed specially. If the buffer's name is in this list, `display-buffer' handles the buffer specially. By default, special display means to give the buffer a dedicated frame. If an element is a list, instead of a string, then the CAR of the list is the buffer name, and the rest of the list says how to create the frame. There are two possibilities for the rest of the list. It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function's first argument is always the buffer to be displayed; the arguments from the list come after that.) - User Option: special-display-regexps A list of regular expressions that specify buffers that should be displayed specially. If the buffer's name matches any of the regular expressions in this list, `display-buffer' handles the buffer specially. By default, special display means to give the buffer a dedicated frame. If an element is a list, instead of a string, then the CAR of the list is the regular expression, and the rest of the list says how to create the frame. See above, under `special-display-buffer-names'. - Variable: special-display-function This variable holds the function to call to display a buffer specially. It receives the buffer as an argument, and should return the window in which it is displayed. The default value of this variable is `special-display-popup-frame'. - Function: special-display-popup-frame buffer &rest args This function makes BUFFER visible in a frame of its own. If BUFFER is already displayed in a window in some frame, it makes the frame visible and raises it, to use that window. Otherwise, it creates a frame that will be dedicated to BUFFER. If ARGS is an alist, it specifies frame parameters for the new frame. If ARGS is a list whose CAR is a symbol, then `(car ARGS)' is called as a function to actually create and set up the frame; it is called with BUFFER as first argument, and `(cdr ARGS)' as additional arguments. This function always uses an existing window displaying BUFFER, whether or not it is in a frame of its own; but if you set up the above variables in your init file, before BUFFER was created, then presumably the window was previously made by this function. - User Option: special-display-frame-alist This variable holds frame parameters for `special-display-popup-frame' to use when it creates a frame. - User Option: same-window-buffer-names A list of buffer names for buffers that should be displayed in the selected window. If the buffer's name is in this list, `display-buffer' handles the buffer by switching to it in the selected window. - User Option: same-window-regexps A list of regular expressions that specify buffers that should be displayed in the selected window. If the buffer's name matches any of the regular expressions in this list, `display-buffer' handles the buffer by switching to it in the selected window. - Variable: display-buffer-function This variable is the most flexible way to customize the behavior of `display-buffer'. If it is non-`nil', it should be a function that `display-buffer' calls to do the work. The function should accept two arguments, the same two arguments that `display-buffer' received. It should choose or create a window, display the specified buffer, and then return the window. This hook takes precedence over all the other options and hooks described above. A window can be marked as "dedicated" to its buffer. Then `display-buffer' will not try to use that window to display any other buffer. - Function: window-dedicated-p window This function returns `t' if WINDOW is marked as dedicated; otherwise `nil'. - Function: set-window-dedicated-p window flag This function marks WINDOW as dedicated if FLAG is non-`nil', and nondedicated otherwise.  File: elisp, Node: Window Point, Next: Window Start, Prev: Choosing Window, Up: Windows Windows and Point ================= Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer. * The window point is established when a window is first created; it is initialized from the buffer's point, or from the window point of another window opened on the buffer if such a window exists. * Selecting a window sets the value of point in its buffer from the window's value of point. Conversely, deselecting a window sets the window's value of point from that of the buffer. Thus, when you switch between windows that display a given buffer, the point value for the selected window is in effect in the buffer, while the point values for the other windows are stored in those windows. * As long as the selected window displays the current buffer, the window's point and the buffer's point always move together; they remain equal. * *Note Positions::, for more details on buffer positions. As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer. - Function: window-point &optional window This function returns the current position of point in WINDOW. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. If WINDOW is `nil', the selected window is used. When WINDOW is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer. Strictly speaking, it would be more correct to return the "top-level" value of point, outside of any `save-excursion' forms. But that value is hard to find. - Function: set-window-point window position This function positions point in WINDOW at position POSITION in WINDOW's buffer.  File: elisp, Node: Window Start, Next: Textual Scrolling, Prev: Window Point, Up: Windows The Window Start Position ========================= Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the "display-start" position of the window (or just the "start"). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line. - Function: window-start &optional window This function returns the display-start position of window WINDOW. If WINDOW is `nil', the selected window is used. For example, (window-start) => 7058 When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any. Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)--for example, to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay. For a realistic example of using `window-start', see the description of `count-lines' in *Note Text Lines::. - Function: window-end &optional window update This function returns the position of the end of the display in window WINDOW. If WINDOW is `nil', the selected window is used. Simply changing the buffer text or moving point does not update the value that `window-end' returns. The value is updated only when Emacs redisplays and redisplay completes without being preempted. If the last redisplay of WINDOW was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns `nil'. If UPDATE is non-`nil', `window-end' always returns an up-to-date value for where the window ends, based on the current `window-start' value. If the saved value is valid, `window-end' returns that; otherwise it computes the correct value by scanning the buffer text. Even if UPDATE is non-`nil', `window-end' does not attempt to scroll the display if point has moved off the screen, the way real redisplay would do. It does not alter the `window-start' value. In effect, it reports where the displayed text will end if scrolling is not required. - Function: set-window-start window position &optional noforce This function sets the display-start position of WINDOW to POSITION in WINDOW's buffer. It returns POSITION. The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using `nil' for NOFORCE, it means you want display to start at POSITION even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window. For example, if point is 1 and you set the start of the window to 2, then point would be "above" the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example: ;; Here is what `foo' looks like before executing ;; the `set-window-start' expression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) => 2 ;; Here is what `foo' looks like after executing ;; the `set-window-start' expression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ---------- If NOFORCE is non-`nil', and POSITION would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus POSITION is not used. - Function: pos-visible-in-window-p &optional position window partially This function returns `t' if POSITION is within the range of text currently visible on the screen in WINDOW. It returns `nil' if POSITION is scrolled vertically or horizontally out of view. Locations that are partially obscured are not considered visible unless PARTIALLY is non-`nil'. The argument POSITION defaults to the current position of point in WINDOW; WINDOW, to the selected window. Here is an example: (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0))  File: elisp, Node: Textual Scrolling, Next: Vertical Scrolling, Prev: Window Start, Up: Windows Textual Scrolling ================= "Textual scrolling" means moving the text up or down though a window. It works by changing the value of the window's display-start location. It may also change the value of `window-point' to keep point on the screen. Textual scrolling was formerly called "vertical scrolling," but we changed its name to distinguish it from the new vertical fractional scrolling feature (*note Vertical Scrolling::). In the commands `scroll-up' and `scroll-down', the directions "up" and "down" refer to the motion of the text in the buffer at which you are looking through the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at text in the middle of a buffer and repeatedly call `scroll-down', you will eventually see the beginning of the buffer. Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view. The textual scrolling functions (aside from `scroll-other-window') have unpredictable results if the current buffer is different from the buffer that is displayed in the selected window. *Note Current Buffer::. - Command: scroll-up &optional count This function scrolls the text in the selected window upward COUNT lines. If COUNT is negative, scrolling is actually downward. If COUNT is `nil' (or omitted), then the length of scroll is `next-screen-context-lines' lines less than the usable height of the window (not counting its mode line). `scroll-up' returns `nil'. - Command: scroll-down &optional count This function scrolls the text in the selected window downward COUNT lines. If COUNT is negative, scrolling is actually upward. If COUNT is omitted or `nil', then the length of the scroll is `next-screen-context-lines' lines less than the usable height of the window (not counting its mode line). `scroll-down' returns `nil'. - Command: scroll-other-window &optional count This function scrolls the text in another window upward COUNT lines. Negative values of COUNT, or `nil', are handled as in `scroll-up'. You can specify which buffer to scroll by setting the variable `other-window-scroll-buffer' to a buffer. If that buffer isn't already displayed, `scroll-other-window' displays it in some window. When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable `minibuffer-scroll-window'. This variable has no effect when any other window is selected. *Note Minibuffer Misc::. When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case, `scroll-other-window' attempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message "Beginning of buffer". - Variable: other-window-scroll-buffer If this variable is non-`nil', it tells `scroll-other-window' which buffer to scroll. - User Option: scroll-margin This option specifies the size of the scroll margin--a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, the window scrolls automatically (if possible) to move point out of the margin, closer to the center of the window. - User Option: scroll-conservatively This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is zero, then redisplay scrolls the text to center point vertically in the window. If the value is a positive integer N, then redisplay scrolls the window up to N lines in either direction, if that will bring point back into view. Otherwise, it centers point. The default value is zero. - User Option: scroll-down-aggressively The value of this variable should be either `nil' or a fraction F between 0 and 1. If it is a fraction, that specifies where on the screen to put point when scrolling down. More precisely, when a window scrolls down because point is above the window start, the new start position is chosen to put point F part of the window height from the top. The larger F, the more aggressive the scrolling. A value of `nil' is equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion. - User Option: scroll-up-aggressively Likewise, for scrolling up. The value, F, specifies how far point should be placed from the bottom of the window; thus, as with `scroll-up-aggressively', a larger value scrolls more aggressively. - User Option: scroll-step This variable is an older variant of `scroll-conservatively'. The difference is that it if its value is N, that permits scrolling only by precisely N lines, not a smaller number. This feature does not work with `scroll-margin'. The default value is zero. - User Option: scroll-preserve-screen-position If this option is non-`nil', the scroll functions move point so that the vertical position of the cursor is unchanged, when that is possible. - User Option: next-screen-context-lines The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example, `scroll-up' with an argument of `nil' scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is `2'. - Command: recenter &optional count This function scrolls the selected window to put the text where point is located at a specified vertical position within the window. If COUNT is a nonnegative number, it puts the line containing point COUNT lines down from the top of the window. If COUNT is a negative number, then it counts upward from the bottom of the window, so that -1 stands for the last usable line in the window. If COUNT is a non-`nil' list, then it stands for the line in the middle of the window. If COUNT is `nil', `recenter' puts the line containing point in the middle of the window, then clears and redisplays the entire selected frame. When `recenter' is called interactively, COUNT is the raw prefix argument. Thus, typing `C-u' as the prefix sets the COUNT to a non-`nil' list, while typing `C-u 4' sets COUNT to 4, which positions the current line four lines from the top. With an argument of zero, `recenter' positions the current line at the top of the window. This action is so handy that some people make a separate key binding to do this. For example, (defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window)  File: elisp, Node: Vertical Scrolling, Next: Horizontal Scrolling, Prev: Textual Scrolling, Up: Windows Vertical Fractional Scrolling ============================= "Vertical fractional scrolling" means shifting the image in the window up or down by a specified multiple or fraction of a line. Starting in Emacs 21, each window has a "vertical scroll position", which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero. The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height. What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image. - Function: window-vscroll &optional window This function returns the current vertical scroll position of WINDOW, If WINDOW is `nil', the selected window is used. (window-vscroll) => 0 - Function: set-window-vscroll window lines This function sets WINDOW's vertical scroll position to LINES. The argument LINES should be zero or positive; if not, it is taken as zero. The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly. The return value is the result of this rounding. (set-window-vscroll (selected-window) 1.2) => 1.13  File: elisp, Node: Horizontal Scrolling, Next: Size of Window, Prev: Vertical Scrolling, Up: Windows Horizontal Scrolling ==================== "Horizontal scrolling" means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a "vertical scroll position", which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero. The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line. Because we read from side to side in the "inner loop", and from top to bottom in the "outer loop", the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of _each line_ to go off screen. Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge. In Emacs 21, redisplay automatically alters the horizontal scrolling of a window as necessary to ensure that point is always visible, if `automatic-hscrolling' is set. However, you can still set the horizontal scrolling value explicitly. The value you specify serves as a lower bound for automatic scrolling, i.e. automatic scrolling will not scroll a window to a column less than the specified one. - Command: scroll-left &optional count This function scrolls the selected window COUNT columns to the left (or to the right if COUNT is negative). The default for COUNT is the window width, minus 2. The return value is the total amount of leftward horizontal scrolling in effect after the change--just like the value returned by `window-hscroll' (below). - Command: scroll-right &optional count This function scrolls the selected window COUNT columns to the right (or to the left if COUNT is negative). The default for COUNT is the window width, minus 2. The return value is the total amount of leftward horizontal scrolling in effect after the change--just like the value returned by `window-hscroll' (below). Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect. - Function: window-hscroll &optional window This function returns the total leftward horizontal scrolling of WINDOW--the number of columns by which the text in WINDOW is scrolled left past the left margin. The value is never negative. It is zero when no horizontal scrolling has been done in WINDOW (which is usually the case). If WINDOW is `nil', the selected window is used. (window-hscroll) => 0 (scroll-left 5) => 5 (window-hscroll) => 5 - Function: set-window-hscroll window columns This function sets the number of columns from the left margin that WINDOW is scrolled from the value of COLUMNS. The argument COLUMNS should be zero or positive; if not, it is taken as zero. Fractional values of COLUMNS are not supported at present. The value returned is COLUMNS. (set-window-hscroll (selected-window) 10) => 10 Here is how you can determine whether a given position POSITION is off the screen due to horizontal scrolling: (defun hscroll-on-screen (window position) (save-excursion (goto-char position) (and (>= (- (current-column) (window-hscroll window)) 0) (< (- (current-column) (window-hscroll window)) (window-width window)))))  File: elisp, Node: Size of Window, Next: Resizing Windows, Prev: Horizontal Scrolling, Up: Windows The Size of a Window ==================== An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of `|' characters that separates side-by-side windows. The following three functions return size information about a window: - Function: window-height &optional window This function returns the number of lines in WINDOW, including its mode line. If WINDOW fills its entire frame, this is typically one less than the value of `frame-height' on that frame (since the last line is always reserved for the minibuffer). If WINDOW is `nil', the function uses the selected window. (window-height) => 23 (split-window-vertically) => # (window-height) => 11 - Function: window-width &optional window This function returns the number of columns in WINDOW. If WINDOW fills its entire frame, this is the same as the value of `frame-width' on that frame. The width does not include the window's scroll bar or the column of `|' characters that separates side-by-side windows. If WINDOW is `nil', the function uses the selected window. (window-width) => 80 - Function: window-edges &optional window This function returns a list of the edge coordinates of WINDOW. If WINDOW is `nil', the selected window is used. The order of the list is `(LEFT TOP RIGHT BOTTOM)', all elements relative to 0, 0 at the top left corner of the frame. The element RIGHT of the value is one more than the rightmost column used by WINDOW, and BOTTOM is one more than the bottommost row used by WINDOW and its mode-line. If a window has a scroll bar, the right edge value includes the width of the scroll bar. Otherwise, if the window has a neighbor on the right, its right edge value includes the width of the separator line between the window and that neighbor. Since the width of the window does not include this separator, the width does not usually equal the difference between the right and left edges. Here is the result obtained on a typical 24-line terminal with just one window: (window-edges (selected-window)) => (0 0 80 23) The bottom edge is at line 23 because the last line is the echo area. If WINDOW is at the upper left corner of its frame, then BOTTOM is the same as the value of `(window-height)', RIGHT is almost the same as the value of `(window-width)', and TOP and LEFT are zero. For example, the edges of the following window are `0 0 8 5'. Assuming that the frame has more than 8 columns, the last column of the window (column 7) holds a border rather than text. The last row (row 4) holds the mode line, shown here with `xxxxxxxxx'. 0 _______ 0 | | | | | | | | xxxxxxxxx 4 7 In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are `0 0 4 3' and the edges of the right window are `4 0 8 3'. ___ ___ | | | | | | xxxxxxxxx 0 34 7  File: elisp, Node: Resizing Windows, Next: Coordinates and Windows, Prev: Size of Window, Up: Windows Changing the Size of a Window ============================= The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows. - Command: enlarge-window size &optional horizontal This function makes the selected window SIZE lines taller, stealing lines from neighboring windows. It takes the lines from one window at a time until that window is used up, then takes from another. If a window from which lines are stolen shrinks below `window-min-height' lines, that window disappears. If HORIZONTAL is non-`nil', this function makes WINDOW wider by SIZE columns, stealing columns instead of lines. If a window from which columns are stolen shrinks below `window-min-width' columns, that window disappears. If the requested size would exceed that of the window's frame, then the function makes the window occupy the entire height (or width) of the frame. If there are various other windows from which lines or columns can be stolen, and some of them specify fixed size (using `window-size-fixed', see below), they are left untouched while other windows are "robbed." If it would be necessary to alter the size of a fixed-size window, `enlarge-window' gets an error instead. If SIZE is negative, this function shrinks the window by -SIZE lines or columns. If that makes the window smaller than the minimum size (`window-min-height' and `window-min-width'), `enlarge-window' deletes the window. `enlarge-window' returns `nil'. - Command: enlarge-window-horizontally columns This function makes the selected window COLUMNS wider. It could be defined as follows: (defun enlarge-window-horizontally (columns) (enlarge-window columns t)) - Command: shrink-window size &optional horizontal This function is like `enlarge-window' but negates the argument SIZE, making the selected window smaller by giving lines (or columns) to the other windows. If the window shrinks below `window-min-height' or `window-min-width', then it disappears. If SIZE is negative, the window is enlarged by -SIZE lines or columns. - Command: shrink-window-horizontally columns This function makes the selected window COLUMNS narrower. It could be defined as follows: (defun shrink-window-horizontally (columns) (shrink-window columns t)) - Command: shrink-window-if-larger-than-buffer &optional window This command shrinks WINDOW to be as small as possible while still showing the full contents of its buffer--but not less than `window-min-height' lines. If WINDOW is not given, it defaults to the selected window. However, the command does nothing if the window is already too small to display the whole text of the buffer, or if part of the contents are currently scrolled off screen, or if the window is not the full width of its frame, or if the window is the only window in its frame. - Variable: window-size-fixed If this variable is non-`nil', in any given buffer, then the size of any window displaying the buffer remains fixed unless you explicitly change it or Emacs has no other choice. (This feature is new in Emacs 21.) If the value is `height', then only the window's height is fixed; if the value is `width', then only the window's width is fixed. Any other non-`nil' value fixes both the width and the height. The usual way to use this variable is to give it a buffer-local value in a particular buffer. That way, the windows (but usually there is only one) displaying that buffer have fixed size. Explicit size-change functions such as `enlarge-window' get an error if they would have to change a window size which is fixed. Therefore, when you want to change the size of such a window, you should bind `window-size-fixed' to `nil', like this: (let ((window-size-fixed nil)) (enlarge-window 10)) Note that changing the frame size will change the size of a fixed-size window, if there is no other alternative. The following two variables constrain the window-size-changing functions to a minimum height and width. - User Option: window-min-height The value of this variable determines how short a window may become before it is automatically deleted. Making a window smaller than `window-min-height' automatically deletes it, and no window may be created shorter than this. The absolute minimum height is two (allowing one line for the mode line, and one line for the buffer display). Actions that change window sizes reset this variable to two if it is less than two. The default value is 4. - User Option: window-min-width The value of this variable determines how narrow a window may become before it is automatically deleted. Making a window smaller than `window-min-width' automatically deletes it, and no window may be created narrower than this. The absolute minimum width is one; any value below that is ignored. The default value is 10.